A need for encasing a tubular member of non-linear configuration in an outer member in spaced sleeved relationship thereto sometimes arises in the art of fabricating visual display systems such as a sign which comprises transparent tubular members in sleeved relationship and configured in script form. The sign is incorporated in a liquid circulating system wherein colored liquids are circulated through the passage formed between the sleeved tubular members of the sign. Such a display system, as disclosed in U.S. Pat. No. 2,029,183 and in applicant's co-pending application, Ser. No. 07/663,152, filed Mar. 1, 1991, now U.S. Pat. No. 5,075,992, typically comprises a luminous tubing in a configuration of complex geometric form, such as script, which tubing is concentrically disposed within an outer pipe of transparent material. A liquid circulating system connected to the ends of the outer pipe is arranged to circulate colored liquids in sequence through the passage formed between the sleeved tubular members. Since the outer member must be transparent, it must therefore retain a very high surface finish on both its interior and exterior surfaces of a quality comparable to that of transparent optical materials. In addition, the outer member must be chemically resistant and stain resistant to the liquids which are circulated through the display system.
Because of the complex geometry typically associated with a sign in the form of a luminous tubing in script configuration, the conventional construction methods and materials used in constructing a tube assembly wherein the tubes are of linear configuration and wherein one tube is disposed internally of another in concentric relation thereto, are not adequate. The materials employed in these prior art methods are almost always opaque and under the associated conditions of manufacture do not provide highly smooth surface finishes of a quality appropriate for most visual display systems. Furthermore, materials which might be used to provide for transparency are frequently ill-suited for other reasons such as inappropriate melting temperatures or the like.